docs: def _readsie(self, pos):
          """Return interpretation of next bits as a signed interleaved exponential-Golomb code.
  
          Advances position to after the read code.
  
          Raises ReadError if the end of the bitstring is encountered while
          reading the code.
  
          """
          codenum, pos = self._readuie(pos)
          if not codenum:
              return 0, pos
          try:
              if self[pos]:
                  return -codenum, pos + 1
              else:
                  return codenum, pos + 1
          except IndexError:
              raise ReadError("Read off end of bitstring trying to read code.")